It's also psychologically easier to manage. People have an easier time building a schedule where they do or don't eat and holding it (say, by skipping breakfast) than they do managing counting calories around things like "I went out to dinner and probably ate too much".

Binary choices (should I eat right now?) take much less cognitive overhead than spectral choices (What should I eat? How much of it? If I eat X and Y now will I have the capacity to eat Z later?)